This disclosure pertains, inter alia, to radiation-detection devices, such as thermal infrared sensors and the like. The sensors can be of several types. One type encompasses so-called electrical-capacitance radiation detectors that convert incident radiation, such as infrared radiation, to a corresponding physical displacement of two opposing electrodes relative to each other and xe2x80x9cread outxe2x80x9d the displacement as a corresponding change in electrical capacitance. Another type encompasses so-called optical-readout radiation detectors that convert incident radiation, such as infrared radiation, to a corresponding physical displacement and xe2x80x9cread outxe2x80x9d the displacement as a corresponding change in readout light.
Radiation detectors are useful for a wide variety of contemporary applications in various fields of endeavor. Various types of conventional radiation detectors are sensitive to different wavelengths of incident radiation. For example, many conventional radiation detectors are sensitive to infrared (IR) radiation and are useful for surveillance, security, heat sensing, imaging, and other applications.
An exemplary IR-radiation detector is disclosed in U.S. Pat. No. 5,623,147 to Baert et al. This conventional detector is a so-called xe2x80x9celectrical capacitancexe2x80x9d type of detector. The detector comprises a substrate, a first bimetallic arm, and a second bimetallic arm. One end of each of the first and second bimetallic arms is mounted to the substrate. To the other end of the first bimetallic arm is affixed a first capacitor electrode. The second bimetallic arm is parallel to and structured similarly to the first bimetallic arm. To the other end of the second bimetallic arm is affixed a second capacitor electrode that faces the first electrode. A radiation-absorbing layer is thermally coupled to the first bimetallic arm but not to the second bimetallic arm. Each of the first and second bimetallic arms includes two layers made of respective materials having different coefficients of thermal expansion. Each layer extends in a respective plane that is parallel to the plane of the radiation-absorbing film. The first and second bimetallic arms (and respective electrodes) are separated from each other by an air gap extending in a xe2x80x9cstacking directionxe2x80x9d (i.e., a direction normal to the substrate and to the radiation-absorbing layer). Hence, when viewed from a direction normal to the plane of the radiation-absorbing layer (and thus normal to the electrodes of the first and second bimetallic arms), the first and second bimetallic arms overlap each other.
Further regarding the Baert et al. detector, whenever infrared radiation from an object is incident to the radiation-absorbing layer, the radiation is absorbed by the radiation-absorbing layer and converted to heat. The first bimetallic arm deforms (exhibits bending) in response to the heat. The second bimetallic arm exhibits substantially no deformation because essentially no heat absorbed by the radiation-absorbing layer is conducted or otherwise transmitted to the second bimetallic arm. Hence, as the first bimetallic arm deforms from absorption of heat, the gap between the first and second electrodes changes (typically becomes smaller). The magnitude of change of the gap is a function of the quantity of incident infrared radiation absorbed by the radiation-absorbing layer. As the gap changes, the electrical capacitance between the first and second electrodes correspondingly changes.
In the Baert et al. detector, since the second electrode is affixed to the second bimetallic arm (which is structured identically to the first bimetallic arm), whenever the first bimetallic arm deforms from a change in ambient temperature, the second bimetallic arm ideally deforms by the same amount. Thus, ideally, the relative positional relationship between the first and second electrodes is unchanged with a change in ambient temperature. Purportedly, with such a configuration, infrared radiation from an object is detected accurately without the electrical capacitance between the first and second electrodes changing or being affected adversely by changes in ambient temperature. Also, especially with control of the substrate temperature being unaffected by changes in ambient temperature, strict temperature control of the overall detector is unnecessary.
However, actual fabrication and operation experience with the Baert et al. detector reveals that the detector is not without significant problems. For example, in the Baert et al. detector, the first and second bimetallic arms are disposed so as to overlap each other when viewed from a normal direction, as noted above. As a result, during manufacture of the detector, one bimetallic arm must be produced displaced above the substrate and the other bimetallic arm must be produced displaced above the first bimetallic arm. Hence, the respective fabrication steps for forming the bimetallic arms must be performed separately, which substantially increases costs.
More importantly, because the first and second bimetallic arms are produced in separate fabrication steps, it is difficult to establish a desired xe2x80x9cbaseline gapxe2x80x9d (existing gap whenever no infrared radiation is incident on the detector) between the first and second electrodes. It also is difficult to impossible to establish a consistent baseline gap from one pixel to another on the same radiation detector. The two film layers that comprise each bimetallic arm are formed extremely thin to decrease their thermal capacity and to increase responsiveness of the bimetallic arms. But, these conditions render the bimetallic arms susceptible to bending upward or downward relative to the substrate in response to residual internal stress in either film. Stress in a film can result from minute changes in film-forming conditions from one fabrication step to another that are extremely difficult to control to a sufficiently strict degree. Furthermore, because the bimetallic arms are produced in separate fabrication steps, the respective initial deformed conditions of the first and second bimetallic arms are different. Again, this difference makes it difficult to establish a desired positional relationship (e.g., gap) of the first and second electrodes. Hence, the desired sensitivity and dynamic range of infrared detection cannot be obtained on a sufficiently consistent basis to be practical.
Furthermore, the electrical capacitance between the first and second electrodes is inversely proportional to the distance between the first and second electrodes. Hence, the capacitance increases with decreasing gap. Also, the capacitance increases with changes in temperature caused by incident infrared radiation. Hence, the narrower the gap, the greater the sensitivity with which infrared radiation can be detected. But, if the electrodes were to touch each other, then any changes that may further increase the capacitance between the electrodes would not occur, thereby restricting the dynamic range.
It is preferable that the gap between the electrodes be as narrow as possible without allowing the electrodes to touch each other. But, due to the difficulty in setting the gap to a desired dimension, as discussed above, the gap usually is made larger than desired or it is accepted that the electrodes are vulnerable to touching each other, thereby decreasing detection sensitivity and undesirably limiting the dynamic range of the detector.
Another difficulty with manufacturing the first and second bimetallic arms in separate fabrication steps, as taught by Baert et al., is the difficulty in sufficiently suppressing changes in electrical capacitance between the electrodes due to changes in ambient temperature. Namely, in fabricating the first and second bimetallic arms by conventional methods, the characteristics of the films (e.g., film thickness) comprising the bimetallic arms cannot be maintained completely identical in both bimetallic arms. Since the characteristics of arm deformation caused by changes in temperature depend upon the film characteristics, the respective deformations of the first and second arms from temperature changes are not identical. This difference causes a corresponding change in capacitance between the electrodes with changes in ambient temperature. The capacitance change, unfortunately, can be relatively large, which renders the conventional device impractical for many uses.
Another exemplary type of IR-radiation detector is disclosed in U.S. Pat. No. 6,080,988 to Ishizuya et al. This detector is a so-called xe2x80x9coptical readoutxe2x80x9d type of detector. The detector comprises a substrate, a first displaceable member supported by the substrate, and a second displaceable member supported by the substrate. A readout-light half-mirror is fixed with respect to the first displaceable member, and a readout-light reflector fixed with respect to the second displaceable member. A radiation absorber, that absorbs radiation such as IR radiation, is thermally connected to the first displaceable member but substantially not thermally connected to the second displaceable member.
Each of the first and second displaceable members comprises two layers of respective materials having different coefficients of thermal expansion, in the manner of a bimetallic structure. The direction of superposition of the two layers is normal to the substrate. The first and second displaceable members are disposed parallel to each other, but spaced apart from each other in the normal direction, so as to be superposed with each other when viewed in the normal direction. The first and second displaceable members have the same configuration, for example, so that the difference in the coefficients of thermal expansion of the upper and lower layers of the first displaceable member is the same as the difference in the coefficients of thermal expansion of the upper and lower layers of the second displaceable member.
The readout-light half-mirror and the readout-light reflector are disposed so as to face each other. They are configured to receive the readout light (e.g., visible light), impart a change to the received light, and produce an emitted readout light having an interference characteristic corresponding to the relative displacement between the readout-light half-mirror and the readout-light reflector.
Whenever IR radiation or the like from an object is incident on the radiation absorber, the rays of incident radiation are absorbed by the radiation absorber and converted into heat. The heat is conducted to the first displaceable member, which exhibits a bending response. The heat is substantially not transmitted to the second displaceable member. As a result, the second displaceable member does not bend, and the distance between the readout-light half-mirror and the readout-light reflector varies as a function of the amount of incident radiation. Accordingly, the radiation from the object can be detected as the intensity of interference light returning from the readout-light half-mirror and the readout-light reflector that were irradiated with readout light.
With this conventional optical-readout type of radiation detector, as with the conventional electrical capacitance type of radiation detector summarized above, the first and second displaceable members are disposed such that they exactly superpose each other when viewed in the normal direction. As a result, the same problems encountered during manufacture of the conventional electrical capacitance type of radiation detector are also encountered during manufacture of the conventional optical-readout type of radiation detector. More specifically, the first and second displaceable members are produced in separate manufacturing steps, which makes it difficult to set a proper and consistent gap (xe2x80x9cinitial gapxe2x80x9d) between the readout-light half-mirror and the readout-light reflector whenever no radiation is incident.
In other words, because this conventional optical-readout radiation detector relies on the principle of interference of readout light, a change in interference intensity of readout light varies periodically as a sinusoidal waveform with changes in the gap between the readout-light half-mirror and the readout-light reflector. Consequently, the radiation-detection characteristics of the detector, such as the change in interference intensity of the readout light (i.e., sensitivity of radiation detection), vary depending upon the initial gap. This variation arises regardless of whether the incident radiation increases or decreases steadily or reverses at some point, or whether the interference intensity of the readout light increases or decreases with respect to an increase in the amount of incident radiation. Hence, desired radiation-detection performance cannot be obtained with this detector because of the difficulty in setting the initial gap to a desired value.
Also, because the first and second displaceable members are produced in separate manufacturing steps, it is very difficult in actual practice to adequately suppress changes in the gap caused by changes in ambient temperature.
In view of the shortcomings of the prior art as summarized above, this invention provides, inter alia, radiation detectors including one or more pixels, in which a pixel includes first and second xe2x80x9ceffecting elementsxe2x80x9d between which a gap can be set to a desired distance consistently from one pixel to the next. The subject detectors provide desired sensitivity characteristics and a desired dynamic range in radiation detection. The subject radiation detectors also exhibit superior suppression of changes in the xe2x80x9ceffecting parameterxe2x80x9d between the effecting elements due to changes in ambient temperature, thereby providing improved detection accuracy than conventional detectors.
According to a first aspect of the invention, radiation detectors are provided that achieve the objects noted above. Such a radiation detector includes a substrate on which at least one xe2x80x9cunit pixelxe2x80x9d (detection unit) is formed. An embodiment of such a radiation detector comprises first and second displaceable members attached to the substrate. The displaceable members have similar respective thermally bimorphous structures. A first xe2x80x9ceffecting elementxe2x80x9d is attached to the first displaceable member, and a second xe2x80x9ceffecting elementxe2x80x9d is attached to the second displaceable member such that at least a portion of the second effecting element faces the first effecting element.
One exemplary xe2x80x9ceffecting elementxe2x80x9d is an electrode or analogous component that can be used to impart a change to a measurable electrical parameter. For example, a change in distance between two electrodes yields a change in electrical capacitance that can be measured. Another exemplary effecting element is an optical component such as a reflector or analogous component that can be used to impart a change to a measurable optical parameter. For example, the first and second effecting elements can be reflectors of a xe2x80x9creadout light,xe2x80x9d wherein a change in distance between the two reflectors yields a change in optical interference of readout light that can be measured. In the foregoing examples, the electrical capacitance and optical interference are respective exemplary xe2x80x9ceffecting parameters.xe2x80x9d
In this embodiment, the radiation detector includes a radiation absorber configured to absorb incident radiation (e.g., IR radiation, ultraviolet radiation, visible radiation, X-rays) to be detected. The radiation absorber is thermally coupled to the first displaceable member but substantially not to the second displaceable member. As a result, the radiation absorber, when heated by absorption of incident radiation, transfers heat to the first displaceable member but substantially not to the second displaceable member. Each of the first and second displaceable members includes at least a first and a second layer laminated together in a xe2x80x9cstacking directionxe2x80x9d (normal to the substrate) to form the respective thermally bimorphous structure. The first and second layers are formed of respective first and second materials having different respective coefficients of thermal expansion so as to cause the respective displaceable member to exhibit a bending response when heated. The bending response occurring in one displaceable member (typically the first displaceable member thermally coupled to the radiation absorber) but substantially not in the other results in a corresponding change in a gap distance between the first and second effecting elements. (The amount of bending exhibited by the displaceable member exhibiting xe2x80x9csubstantiallyxe2x80x9d no bending response does not, within an acceptable tolerance, alter the apparent quantity of radiation corresponding to the bending exhibited by the displaceable member coupled to the radiation absorber.)
The first and second effecting elements are configured to allow measurement of the effecting parameter, which exhibits a change with a corresponding change in the gap distance. In addition, the first and second displaceable members are disposed so as not to overlap each other when viewed in the stacking direction.
As noted above, the first and second effecting elements can be first and second electrodes, wherein the first and second electrodes can be configured to allow an electrical capacitance to be measured between them. Alternatively, for example, the first and second effecting elements can be a reflector and half-mirror, respectively, of a readout light.
The first and second displaceable members desirably are situated relative to each other such that the first and second layers of each are formable simultaneously during respective fabrication steps. Further desirably, the second displaceable member is substantially parallel to the first displaceable member.
In radiation detectors in which the effecting parameter is electrical capacitance, a first electrode is attached to the first displaceable member, and a second electrode is attached to the second displaceable member such that at least a portion of the second electrode faces the first electrode. The radiation absorber, when heated by absorption of incident radiation, transfers heat to the first displaceable member but substantially not to the second displaceable member. The resulting bending response in the first displaceable member but substantially not in the second displaceable member results in a change in a gap distance between the first and second electrodes. The change in gap produces a corresponding change in an electrical parameter (e.g., capacitance) of the first and second electrodes. The first and second displaceable members are disposed so as not to overlap each other when viewed in the stacking direction.
In radiation detectors in which the effecting parameter is an optical parameter, a particularly advantageous parameter is optical interference of a readout light, wherein a particular change in interference corresponds to a respective amount of absorbed radiation. A first optically effecting element is attached to the first displaceable member, and a second optically effecting element is attached to the second displaceable member. The first and second optically effecting elements receive readout light, impart a change to the readout light corresponding to the relative displacement between the first and second optically effecting elements, and emit the changed readout light.
The first and second displaceable members desirably are situated relative to each other such that the first and second layers of each of the first and second displaceable members are formable simultaneously during respective steps. As a result, the first and second displaceable members are situated such that they do not overlap each other when viewed from the stacking direction. (As noted above, the xe2x80x9cstacking directionxe2x80x9d is normal to the substrate. The xe2x80x9cstackingxe2x80x9d referred to is the stacking or lamination of the first and second layers of the displaceable members. Hence, the stacking direction is the direction in which the second layer is formed relative to the first layer.) xe2x80x9cFormable simultaneouslyxe2x80x9d as used above means that, for example, the first (also termed xe2x80x9clowerxe2x80x9d) layer of both displaceable members is formed during a single fabrication step. Similarly, the second (also termed xe2x80x9cupperxe2x80x9d) layer of both displaceable members is formed during a different, but nevertheless single, fabrication step.
By fabricating the first and second displaceable members in the manner summarized above, even if the first and second displaceable members should exhibit an initial warp due to stress in one or both the first and second layers, the degree of warp of both displaceable members is substantially identical. Consequently, the xe2x80x9cbaselinexe2x80x9d gap distance between the first and second effecting elements is unchanged by the initial warp. (A xe2x80x9cbaselinexe2x80x9d gap distance is the distance between the first and second effecting elements whenever the subject pixel is not receiving any significant amount of incident radiation to be measured.) Desirably, the first and second displaceable members are situated close to each other, such as laterally adjacent each other (and hence parallel to each other) on the substrate so as to reduce further any relative displacements of the first and second displaceable members due to stress arising at one location during layer formation but not at another location.
Another advantage in forming the first and second layers during the same respective fabrication steps is that any differences in layer characteristics (e.g., layer thickness) of the first and second displaceable members are reduced to insignificant levels. Consequently, differences in bending characteristics of the first and second displaceable members due to temperature changes are considerably reduced compared to conventional radiation detectors. Hence, even if the substrate temperature is not controlled strictly during use of the radiation detector, changes in the effecting parameter between the first and second effecting elements due to changes in ambient temperature are reduced appreciably, compared to conventional radiation detectors. As a result, incident radiation is detected with greater accuracy than obtainable using a conventional radiation detector. Again, the first and second displaceable members desirably are situated adjacent each other to avoid stress differences from one location to another on the substrate.
When using a radiation detector according to the invention, the effects of changes in ambient temperature can be eliminated by placing the radiation detector in a vacuum chamber or by strictly controlling substrate temperature during use of the detector. Even under such conditions, the second displaceable member continues to preserve the gap distance between the first and second electrodes whenever no radiation to be measured is incident to the radiation absorber.
The radiation detector of this embodiment further can comprise a radiation reflector. In such a configuration, the radiation absorber reflects a portion of radiation incident to it. In general, the radiation reflector desirably is situated relative to the radiation absorber so as to define a gap of substantially nxcex0/4 between the radiation absorber and the radiation reflector. In this expression, n is an odd integer and xcex0 is the center (median) wavelength of a wavelength band of radiation detectable by the radiation detector. Hence, for example, whenever radiation is incident to the radiation absorber from an opposite side of the radiation reflector, part of the incident radiation is absorbed by the radiation absorber, while the remainder is reflected by the radiation reflector. The latter reflected radiation is reflected back and forth in the gap between the radiation absorber and the radiation reflector to produce interference. Since the gap is roughly an odd-integer multiple of one-fourth of the central (median) wavelength of the desired wavelength band of incident radiation, radiation absorption by the radiation absorber is maximized according to the xe2x80x9coptical cavityxe2x80x9d principle. This increases the efficiency of radiation absorption and detection even with reduction in the thickness and/or thermal capacity of the radiation absorber.
By way of example, the percentage of incident radiation reflected from the radiation absorber is approximately 33% (approximately ⅓), to increase further the percentage of radiation absorbed at the radiation absorber.
In embodiments comprising first and second electrodes that operate on the principle of electrical capacitance, the radiation reflector desirably is one of the first and second electrodes. With such a configuration, the radiation absorber is situated in the stacking direction relative to the first and second electrodes. In addition to simplifying the overall structure of the radiation detector, disposing the radiation absorber in the stacking direction increases the respective surface areas of the radiation absorber and/or of the electrodes, thereby improving detector sensitivity. The first and second electrodes and the radiation absorber can be aligned with each other and arranged in the stacking direction in an order of: (a) radiation absorber, first electrode, then second electrode, or (b) radiation absorber, second electrode, then first electrode. In either of these configurations, the first displaceable member, when heated, exhibits a bending response that that displaces the second electrode away from the first electrode. The bending response also can be characterized by a so-called xe2x80x9cknee characteristic,xe2x80x9d in which sensitivity of the detector at room temperature to incident radiation is relatively high while sensitivity at higher temperatures is relatively low. In addition, by situating the first electrode between (in the stacking direction) the radiation absorber and the second electrode, even though the radiation absorber is thermally coupled (and consequently also mechanically coupled) to the first electrode, circumstances can be avoided in which the bending range of the first displaceable member is restricted by the radiation absorber touching the second electrode, or similar conditions. This allows the dynamic range of detection to be enlarged appreciably over conventional radiation detectors.
The first effecting element desirably comprises a planar portion (desirably parallel to the substrate) and a side portion extending at least partially around the periphery of the planar portion. Similarly, the second effecting element comprises a planar portion and a side portion that extends at least partially around the periphery of the planar portion. By configuring both effecting elements with respective planar portions and side portions, the effecting elements are reinforced structurally by the side portions. This allows the thickness of each effecting element to be reduced, with concomitant reductions in the respective thermal capacities of the effecting elements, without compromising strength. The respective side portions can be configured to extend away from each other, thereby preventing the side portions from interfering with each another during instances in which the gap between the first and second effecting elements is narrowed. This, in turn, allows the gap between the first and second effecting elements to be made narrower, with accompanying increases in detector sensitivity compared to conventional detectors.
One of the first and second effecting elements can be affixed via a support frame to the respective first or second displaceable member. The support frame desirably is made of a thermally insulative material and comprises a planar portion and a side portion extending from the planar portion along at least a portion of the periphery of the planar portion. The side portion serves to strengthen the planar portion of the support frame in a manner as described above with respect to the first and second effecting elements.
Radiation-detector embodiments comprising first and second electrodes can further comprise an electrically insulative film situated xe2x80x9cbetweenxe2x80x9d the first electrode and the second electrode. E.g., the insulative film can be situated on one or the other of the electrodes. The insulative film serves to prevent electrical shorts between the first and second electrodes even whenever the gap between the electrodes is reduced to zero. The total surface area of the insulative film desirably is low relative to the area of either of the electrodes to avoid significant alteration of the thermal capacity of the respective electrode. Hence, the insulating film can be configured as small regions (xe2x80x9cspotsxe2x80x9d) provided at multiple disparate locations.
The radiation detector further can comprise first and second legs, wherein the first displaceable member is mounted to the substrate via the first leg, and the second displaceable member is mounted to the substrate via the second leg. As described in detail herein, each leg has a respective length direction, a start point, and an end point. With respect to the first leg, the distance along the respective length direction from the respective start point to the respective end point can be substantially equal to, with respect to the second leg, the distance along the respective length direction from the respective start point to the respective end point. By configuring these distances to be equal, the elevations and angles (relative to the substrate) of the respective end points of the first and second legs (and consequently, the respective start points of the first and second displaceable members) can be kept equal, even whenever the first and second legs are initially warped from stress generated during fabrication.
In this configuration, the end point of the first leg can be located in the first displaceable member, and the end point of the second leg can be located in the second displaceable member. The xe2x80x9cstart point of a displaceable memberxe2x80x9d means an edge point on the substrate side of the respective displaceable member, or alternatively an edge point on the effecting-element side of the respective displaceable member. The lengths desirably are equal because, in such a configuration, the angles at the end points of the first and second displaceable members, relative to the substrate, are equal in an initial state of the detector in which there is no radiation incident on the detector.
Alternatively, with respect to the second leg, the distance along the respective length direction from the respective start point to the respective end point can be shorter than, with respect to the first leg, a distance along the respective length direction from the respective start point to the respective end point. This modification includes configurations in which the second leg has zero length, along the length direction, between the start point and the end point. These configurations are especially effective in instances in which the first and second legs are not warped, wherein the respective elevations (above the substrate) and angles at the respective end points of the first and second legs (and, consequently, the start points of the first and second displaceable members) are equal. By reducing the length of the second leg, even to zero length, the area normally occupied by the second leg is eliminated.
In yet another alternative configuration, the start point of the first displaceable member and the start point of the second displaceable member have substantially identical positions when viewed from the width direction of the first and second displaceable members. In such a configuration, the heights of the first and second displaceable members, relative to the substrate, are equal in an initial state of the detector in which no radiation is incident on the detector. This can be advantageous because the relative positional relationship between the first and second effecting elements is virtually unchanged with changes in ambient temperature.
In yet another alternative configuration, the start point of the first displaceable member and the start point of the second displaceable member are shifted relative to each other to form a gap between the first and second displaceable members. The gap is narrowed when viewed from the width direction of the first and second displaceable members. With such a configuration, the gap distance between the first and second effecting elements can be made very narrow, which serves to increase the detection sensitivity of the radiation detector.
The radiation detector can be configured such that the first and second legs, the first and second displaceable members, the first and second effecting elements, and the radiation absorber are disposed in the stacking direction with respective intervening spaces therebetween. With such a configuration, the respective surface areas of the radiation absorber and/or both effecting elements inside any given area can be increased, thereby improving detection sensitivity. However, the overall structure does not exhibit substantial horizontal xe2x80x9cspread,xe2x80x9d which allows an increase in fill factor without sacrificing strength.
Any of the radiation detectors according to the invention can include one or multiple unit pixels. In detectors comprising multiple unit pixels, the unit pixels may be arranged one- or two-dimensionally. Detectors comprising only one pixel can be used to detect the presence or absence of radiation. Detectors comprising multiple pixels (especially arranged in two dimensions) can be used to detect images.
In embodiments including first and second optically effecting elements wherein one of the optically effecting elements is a readout-light reflector, the other optically effecting element can be a half-mirror that faces the reflector. The xe2x80x9chalf-mirrorxe2x80x9d is an element that reflects only part of the readout-light radiation incident to it. In this configuration, the reflector and half-mirror reflect the received readout light and produce therefrom an interference light. Alternatively, both the first and second optically effecting elements can be respective reflectors, wherein the reflectors collectively constitute a reflection-type diffraction grating for reflecting the received readout light as diffracted light.
According to another aspect of the invention, methods are provided for fabricating, on a substrate, a radiation detector including at least one unit pixel. In an embodiment of such a method, a first layer-forming step comprises forming a first layer, of a first material having a respective coefficient of thermal expansion, of each of first and second displaceable members. In a second layer-forming step, a second layer, of a second material having a respective coefficient of thermal expansion that is different from the coefficient of thermal expansion of the first material, is formed of each of the first and second displaceable members to form respective thermally bimorphous structures in which the respective first and second layers are laminated together. A first effecting element is formed, attached to the first displaceable member. A second effecting element also is formed, attached to the second displaceable member such that at least respective portions of the first and second effecting elements face each other in a stacking direction with a space therebetween. Also, the effecting elements are formed such that an effecting parameter associated therewith can be measured (e.g., electrical capacitance or interference of received readout light). A radiation absorber is formed in a manner and location such that the radiation absorber is thermally coupled to the first displaceable member but not to the second displaceable member. The radiation absorber is formed of a material that absorbs incident radiation that causes heating of the radiation absorber with resultant conduction of the heat to the first displaceable member.
The first and second effecting elements and the radiation absorber can be formed in any of various orders of steps. One example order is, from the substrate in a stacking direction, first effecting element, second effecting element, then radiation absorber. Another example order is, from the substrate in a stacking direction, second effecting element, first effecting element, then radiation absorber. Yet another example order is, from the substrate in a stacking direction, radiation absorber, first effecting element, then second effecting element. Yet another example order is, from the substrate in a stacking direction, radiation absorber, second effecting element, then first effecting element.
The foregoing and additional features and advantages of the invention will be more readily apparent from the following detailed discussion, which proceeds with reference to the accompanying drawings.